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Altered phosphorylation and oligomerization of p53 in adenovirus type 12-transformed cells
W T Steegenga1, A Shvarts, T van Laar
1Sylvius Laboratories, Leiden University, The Netherlands.
Abstract:
Loss of function of the tumor-suppressor protein p53 is, in general, either caused by mutation, inducing a conformational change, or by binding to inactivating cellular (e.g. MDM2) or viral (e.g. SV40 large T) proteins. In adenovirus type 12 (Ad12)-transformed cells, p53 is stabilized without detectable binding to the Ad12 E1B/54 kDa protein and still present in a wild-type conformation but contains a mutant-like activity in cellular transformation. In this study we examined whether the changed characteristics of p53 in Ad12-transformed cells are correlated with changes in phosphorylation or complex formation of the protein. By making tryptic phosphopeptide maps we found a significant increase in the phosphorylation of the N-terminus of p53. Furthermore, expression of E1A was found to be essential for the altered phosphorylation, while expression of only Ad12 E1B/54 kDa is sufficient to increase the protein half-life. Additionally, we observed p53 to be present in increased molecular weight complexes in Ad12-transformed cells. We conclude that both the phosphorylation and oligomerization of p53 is changed as a result of Ad12 transformation.
Insights
Adenovirus type 12 (Ad12) alters tumor suppressor protein p53 function in transformed cells. This study reveals Ad12 increases p53 phosphorylation and complex formation, impacting cellular transformation.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- Tumor suppressor protein p53 loss-of-function typically results from mutation or inactivation by viral/cellular proteins.
- In adenovirus type 12 (Ad12)-transformed cells, p53 shows mutant-like activity despite wild-type conformation and lack of direct binding to Ad12 E1B/54 kDa protein.
Purpose of the Study:
- To investigate if altered p53 characteristics in Ad12-transformed cells correlate with changes in phosphorylation or complex formation.
- To elucidate the role of Ad12 viral proteins (E1A and E1B/54 kDa) in p53 modification.
Main Methods:
- Tryptic phosphopeptide mapping was employed to analyze p53 phosphorylation patterns.
- Expression of Ad12 E1A and E1B/54 kDa proteins was manipulated to assess their impact on p53.
Main Results:
- A significant increase in N-terminal phosphorylation of p53 was observed in Ad12-transformed cells.
- Ad12 E1A expression was essential for the altered p53 phosphorylation, while Ad12 E1B/54 kDa alone increased p53 half-life.
- p53 was found in higher molecular weight complexes within Ad12-transformed cells.
Conclusions:
- Adenovirus type 12 transformation alters both the phosphorylation status and oligomerization state of p53.
- These modifications contribute to the altered activity of p53 in cellular transformation processes induced by Ad12.